DE4319648A1 - Sulphidised catalyst containing platinum on activated charcoal - Google Patents

Abstract

The invention relates to a sulphidised catalyst containing platinum on activated charcoal, the activity of which can be considerably increased, with selectivity remaining constant, if an oxidising agent is added to the platinum-containing impregnation solution.

Description

The invention relates to a platinum on activated carbon containing sulfided catalyst and a method for its production.

Sulfided noble metal-containing catalysts are since Manufactured and applied for decades. In DE-PS 21 50 220, for example, a method for Production of such a catalyst described. By sulfiding the noble metal-containing catalyst with a sulfur-containing chemical compound by partial poisoning of the catalyst a higher Selectivity in the desired chemical reaction at usually achieved reduced catalyst activity. About the mechanism of sulfidation itself, nature of the bound sulfur at the catalyst surface as well as the interaction between sulfur, precious metal and Carrier is little known.

Especially in the selective hydrogenation of halogen nitroaromatics (see, for example, not previously published German patent application P 42 18 866.0) and the reductive alkylation (DE-OS 27 36 228) are platinum as a precious metal and Activated carbon as a carrier-containing catalysts other catalyst systems preferred.

The selectivity of these catalysts in these Reactions are caused by partial poisoning Sulfidation improved.  

Sulfur itself or as sulfurizing agent other sulfur-containing compounds, such as H₂S, Dimethylsulfoxide, (NH₄) ₂S, Na₂S, Na₂SO₄, wherein z. B. by the action of a strong acid, such as H₂SO₄ the Sulfur of the sulfur-containing compound released is used. Here are concentrations of 0.1-10 moles of sulfur per mole of platinum, but preferably 0.1-2 moles of sulfur per mole of platinum applied.

Object of the present invention is to provide a generic catalyst and a method to indicate its production, which after partial Poisoning by sulphidation with conventional Sulfidation a significantly improved Catalyst performance as conventional catalysts having.

The task is through a platinum on activated carbon containing sulfided catalyst, the is obtainable by mixing an aqueous solution of a Platinum compound with an aqueous suspension of Activated carbon, heating the mixture to a temperature between 70 and 100 ° C, precipitating the platinum compound with a base and reduce the sparingly soluble Platinum compound with a reducing agent below Maintaining the temperature, filtering off and washing the catalyst thus obtained with distilled water, Treat the catalyst with a sulfiding agent and rewashing the finished catalyst, thereby characterized in that the aqueous solution of platinum compound contains an oxidizing agent.

The platinum content of the finished catalyst can be between 0.1 and 5 wt .-% relative to the activated carbon.  

The addition of an oxidizing agent to the aqueous Solution of the platinum compound before impregnating the powdery carrier of activated carbon leads Surprisingly, to a platinum-containing phase, the the catalyst performance after sulfiding with conventional sulfidation clear improved.

Amazing is the fact that the by Oxidant addition produced catalyst before Sulfidation does not necessarily improve performance in the catalytic reactions.

Suitable activated carbon supports may be acid-activated Coals and steam-activated coals with or without subsequent acid wash can be used. The Catalyst has particularly favorable properties, if the mean particle diameter of the activated carbon 15-30 μm, their specific surface area is larger than 500 m 2 / g, their total pore volume is greater than 0.5 ml / g are and have a pH of more than 7. The Residual ash content of the activated carbon should be less than 2% by weight lie.

To determine the pH, 1 g of activated carbon in 100 ml of water suspended. After stirring for 5 minutes the pH was measured at 25 ° C.

Suitable oxidizing agents may be inorganic Per compounds, such as persulfates and perchlorates, Sodium hypochlorite and alkyl hydroperoxides used be, but especially H₂O₂ in concentrations of 0.1-10.0 mol / mol of platinum, but preferably 0.5-5.0 mol / mol of platinum.  

As suitable sulfidation agents, all of the Prior art known sulfur-containing Connections are used.

When mixing the aqueous solution of the platinum compound with the aqueous suspension of activated carbon can already to a partial precipitation of a sparingly soluble Platinum compound come up, which is on the activated carbon reflected. For complete failure of the platinum as a sparingly soluble compound is the mixture platinum-containing solution and activated carbon suspension one Base added. Suitable bases are sodium carbonate, Sodium hydroxide or potassium hydroxide.

Another object of the invention is to specify a Process for the preparation of the sulphided Catalyst. This task is performed by a procedure dissolved, after which an aqueous solution of Platinum compound with an aqueous suspension of Activated charcoal mixes this mixture to a temperature heated between 70 and 100 ° C, the platinum compound with a base fails and the poorly soluble platinum Connection while maintaining the temperature with a Reducing agent reduced, the resulting Catalyst filtered off and distilled water washes the catalyst with a sulfiding agent treated and washed again. The procedure is thereby characterized in that the aqueous solution of platinum compound contains an oxidizing agent.

The aqueous suspension of activated carbon preferably has a concentration of 5 to 30 wt .-% on. It can various water-soluble platinum compounds be used, has proven particularly useful Hexachloroplatinic acid hexahydrate.  

The oxidizing agent, preferably hydrogen peroxide, becomes in an amount of 0.1-10.0 mol, preferably 0.5-5.0 mol per mole of platinum added to the platinum solution.

Activated carbon suspension and platinum solution are mixed together and with stirring to 70 to 100 ° C. heated before platinum by addition of a base such. B. Sodium carbonate or caustic soda in the form of their heavy soluble compounds on the activated carbon depressed and then unchanged Temperature possibly by adding a reduction by means such as hydrazine, sodium formate, sodium borohydride or formaldehyde, preferably formaldehyde becomes.

The order of addition of platinum solution and base to Activated carbon suspension is not mandatory. So can the Base even before the introduction of the platinum solution of Activated carbon suspension are mixed.

After filtering off and washing the thus obtained Pt / C catalyst, the sulfidation agent such as. B. Dimethyl sulfoxide or ammonium sulfide in combination with a strong acid like sulfuric acid at normal temperature of the aqueous catalyst suspension added.

The sulphided catalyst should have a platinum content from 0.1-5.0, preferably 0.5-3.5 wt .-% and a Sulfur content of 0.1-10, preferably 0.1-2 mol / mol Platinum.

As an alternative to the procedure described above, at the oxidant and platinum-containing solution is added to an activated carbon suspension, the Activated carbon to the oxidant and platinum-containing Be added solution or the oxidizing agent and sprayed platinum-containing solution on the activated carbon become.  

It may be used to stabilize the platinum-containing solution sometimes be beneficial to the solution a mineral acid, such as hydrochloric acid, sulfuric acid or nitric acid, add.

The invention will now be described by way of some examples explained. Example 1 describes the preparation of catalysts of the invention and comparative Catalysts of the prior art. The unsulfided precursors of the catalysts have been reported in Example 2 in a low pressure test for activity examined and compared with each other. In Example 3 were the sulfided catalysts of the invention in a high-pressure test for activity and selectivity investigated and with the comparative catalysts compared.

Example 1: Catalyst Preparation

For all catalysts was used as a carrier activated carbon the following material data is used:

material powdered activated carbon Specific surface BET: 1500 m² / g (ASTM-D-3663) Total pore volume: 1.5 ml / g (ASTM-D-4284) Average grain size 22 μm (ASTM-D-4464) PH value: 10 Ash content: <2%

A) Preparation of the catalyst precursors: (Pt + H₂O₂) / C (without sulfidation)

For the preparation of a catalyst with 3% platinum Loading was 97 g of activated carbon (dry weight) in distilled water at a stirring speed stirred at 300 rpm. This suspension was 12 g of a 25% aqueous solution of hexachloro Platinum hexahydrate (equivalent to 3 g Pt) with 3 ml a 30% aqueous H₂O₂ solution added, corresponding to 2 moles of H₂O₂ per mole of platinum.

Subsequently, the suspension was heated to 80 ° C and precipitating sparingly soluble hydroxides Sodium carbonate added with constant stirring. Finally, to reduce the precipitation Added 1.8 ml of 37% formaldehyde solution. Also During the reduction, the temperature of the Suspension kept constant at 80 ° C. After Reduction, the catalyst was on a suction filter filtered off and washed with distilled water.

B) producing the sulfided inventive Catalyst: (Pt + H₂O₂ + S) / C

For the preparation of a catalyst according to the invention with 3% platinum loading was initially a Prepared catalyst according to Part A and then with Dimethyl sulfoxide according to Example 1 of the DE-PS 21 50 220 sulfided. The total sulfur content of the sulfided catalyst was about 0.4 mole S / mol Pt.  

Catalysts with the same platinum loading but with double or quadruple sulfur content by appropriate multiplication of the Sulfidating agent produced.

Catalysts with different platinum loadings were analogous to the above procedure by simultaneous Multiplication of the amounts of hexachloroplatinic acid, Sodium hydroxide and sulfidation made.

C) Preparation of Comparative Catalysts: Pt / C

For comparison with the catalyst according to the invention were platinum-containing catalysts on activated carbon, as prepared in Example 1, part A or B, however without the addition of H₂O₂.

Example 2: Low Pressure Testing of the Catalyst Precursors (without sulfidation)

The activity of the catalyst precursors was investigated in the hydrogenation of cinnamic acid to dihydrocinnamic acid under the following reaction conditions:
200 mg of catalyst were added to 10 g of cinnamic acid in 120 ml of ethanol and transferred to a 250 ml stirred reactor with gassing stirrer, thermometer and hydrogen feed.

The reactor was first treated with nitrogen at normal pressure thoroughly rinsed. Then it became a constant Hydrogen pressure of 10 mbar above normal at one Set reaction temperature of 25 ° C in the reactor, and the hydrogen via the gassing stirrer (2000 rpm) evenly distributed in the solution.  

To measure the catalyst performance was Catalyst activity in the hydrogenation reaction of Cinnamic acid to dihydrocinnamic acid and in ml Hydrogen / g catalyst / min indicated. As a reaction period for the calculation of this catalyst activity the reaction time was between the 3rd and 8th minute after hydrogen supply.

Table 1 gives the test results of catalysts which according to Example 1, Part A or Part C (without sulfidation) were made again.

Table 1

Table 1 shows that all catalyst precursors have a have comparable activity.

Example 3: High pressure testing of the catalysts (after sulfidation)

Activity and selectivity of the invention Catalysts according to Example 1B were with activity and Selectivity of comparative catalysts from the state the technique of Example 1C in the reductive Hydrogenation of p-aminodiphenylamine (PADPA) with methyl isobutyl ketone (MIBK).  

For this purpose, 3.77 moles of PADPA were added together with 4.63 moles MIBK and 1.38 g of a 3% Pt / C catalyst (corresponding to 0.2% by weight, based on the amount of PADPA) placed in a 2 liter autoclave. The autoclave was closed, first with nitrogen and then with water rinsed and to a hydrogen pressure of 50 bar brought. The reaction mixture was stirred up heated to a temperature of 190 ° C. After 60, 90 and 120 min. Reaction time samples were taken and analyzed.

Table 2 contains the residual contents of the analyzed Samples of unreacted PADPA and the required hydrogenation time to the residual content of PADPA below 2 wt .-% to press.

Table 2

Table 2 shows that by using the Inventive catalysts according to Example 1B a Activity improvement up to 35% above the level of Technique (Example 1C) was achieved. The selectivity was not affected by the H₂O₂ treatment.

Claims (6)

A platinum on activated carbon containing sulfided catalyst obtainable by mixing an aqueous solution of a platinum compound with an aqueous suspension of activated carbon, heating the mixture to a temperature between 70 and 100 ° C, precipitating the platinum compound with a base and reducing the sparingly soluble platinum compound with a reducing agent while maintaining the temperature, filtering off and washing the thus obtained catalyst with distilled water, treating the catalyst with a sulfiding agent and rewashing the finished catalyst, characterized in that the aqueous solution of the platinum compound contains an oxidizing agent. 2. Catalyst according to claim 1, characterized, the activated carbon has a medium particle size diameter of 15 to 30 μm, a specific surface area of more than 500 m² / g, a total pore volume of more than 0.5 ml / g, a residual ash content below 2 wt .-% and has a pH of more than 7.   3. Catalyst according to claim 1 or 2, characterized, that as the oxidizing agent hydrogen peroxide in a Amount of 0.1 to 10.0 mol, preferably 0.5 to 5.0 mol is used per mole of platinum. 4. Process for the preparation of a platinum on active coal containing sulfided catalyst by Mixing an aqueous solution of a platinum compound with an aqueous suspension of activated carbon, Warm this mixture to a temperature between 70 and 100 ° C, precipitation of Platinver Bonding with a base and reducing the hard soluble platinum compound while retaining the Temperature with a reducing agent, filtering off and washing the catalyst thus obtained with distilled water, treating the catalyst with a sulfiding agent and rinsing the finished catalyst, characterized, that the aqueous solution of the platinum compound a Contains oxidizing agent. 5. The method according to claim 4, characterized, the activated carbon has a medium particle size diameter of 15 to 30 μm, a specific surface area of more than 500 m² / g, a total pore volume of more than 0.5 ml / g, a residual ash content below 2 wt .-% and has a pH of more than 7. 6. The method according to claim 4 or 5, characterized, that as the oxidizing agent hydrogen peroxide in a Amount of 0.1 to 10.0 mol, preferably 0.5 to 5.0 mol is used per mole of platinum.